Example 1
A family car of 1400 kg easing off the line at 1.8 m/s²: the gentle push you feel in your back at a green light.
Force F = m·a calculator
Enter mass and acceleration. The calculator computes the net force F = m·a, Newton’s second law. 1400 kg at 1.8 m/s² is 2520 N, a gentle car launch, not distance on a slope.
You know F and want distance at constant a: accelerated motion.
Result
Mass and Acceleration (m/s²). Force shows up here.
How it works
Newton's second law says which net force produces a chosen acceleration: F = m·a. A 1400 kg car at 1.8 m/s² needs 2520 N. At 3.5 m/s² the same mass is 4900 N, not twice 2520, because a did not double. An 80 kg person at g = 9.81 m/s² is about 785 N, the order of weight on a scale, but the mass field stays in kilograms.
The first field is mass. In metric that is kilograms; after the US switch the label may show pounds. The second field is acceleration, usually in m/s², as on the label. The result is in newtons. The switch does not rewrite a number you already typed: change the unit on an empty field, or convert yourself. A comma and a period are the same a: 1,8 and 1.8.
Negative a is braking. Force comes out the other way, with a minus. 1400 kg at −7 m/s² is a deceleration near 0.7 g, not a typing error. Zero kilograms gives zero newtons: there is nothing to push. Negative mass will not run.
The calculator computes one net force for the chosen a. It does not split friction, drag, or a force budget. If a problem gives weight in newtons, divide by g before you fill the first field: 80 N is not 80 kg.
If you already know F and want distance at constant a, open accelerated motion. Here it stays the product of m and a, one number in newtons. Weight F ≈ m·g is the same formula at a = g, but you still type kilograms, not newtons.
Type 1400 and 1.8, click Calculate, and match 2520 N. Then 80 and 9.81: about 785 N. The header symbol does not turn mass into weight.
How to use
- In the first field enter mass. In metric that is kilograms: 1400 for a car, 80 for a person. After the US switch the label may say pounds.
- In the second field enter acceleration in the unit on the label, usually m/s². For example 1.8 for a gentle launch. A minus, for example −7, is braking.
- Click Calculate. The calculator multiplies m by a. 1400 kg and 1.8 m/s² give 2520 N. 80 kg and 9.81 m/s² give about 785 N. 1400 kg and 3.5 m/s² give 4900 N.
- Zero kilograms gives 0 N. Negative a flips the force. That is the net force for this a, not engine power and not a friction sum.
- You know F and want distance at constant a? Open accelerated motion. Scale weight does not go in the mass field. Here it stays F = m·a.
Formula
F = m · a
Mass from the field, a from the field. Result in newtons. Weight does not go in the mass field.
F, m, and a at 1400 kg and 1.8 m/s²
Newton’s second law in this calculator is one net force. 1400 kg at 1.8 m/s² is 2520 N, a gentle launch, not weight typed as mass.
- F
- Net force in newtons: F = m·a. 1400 kg at 3.5 m/s² is 4900 N, not twice 2520, because a did not double.
- m
- Mass in kilograms, first field. 80 kg at 9.81 m/s² is about 785 N of weight, but you still type 80, not 785.
- a
- Acceleration, usually m/s². A minus, for example −7, is braking: force comes out the other way.
- N
- The unit of F. Zero kilograms gives 0 N. 80 N in a problem is not 80 kg: divide by g first.
Real-life examples
Example 2
The same 1400 kg car with the pedal down: 3.5 m/s² and a firm shove into the seat within the first few meters.
Example 3
Emergency stop in a 1400 kg car: 7 m/s² of deceleration (about 0.7 g). The seatbelts lock before you finish gasping.
Example 4
A loaded shopping cart of 35.0 kg pushed up to 0.6 m/s²: sounds trivial, yet you feel every newton in the aisle.
Example 5
Driving a 100 kg barbell out of the bottom of a squat at 2 m/s²: the explosive push that decides the lift.
Example 6
Rider plus bike at 85.0 kg accelerating up a climb at 0.8 m/s². On a gradient, every extra newton is earned.
Example 7
An adult of 70.0 kg simply standing on Earth: g = 9.81 m/s² turns that mass into weight, measured in newtons.
Example 8
Stroller and baby together at 18.0 kg, set moving at 0.5 m/s²: an easy walking start, no jolts for the passenger.
Example 9
A city bus of 12000 kg pulling away from the stop at 1.2 m/s². Standing passengers instinctively grab the handrails.
Example 10
E-scooter plus rider at 90.0 kg accelerating at 1.5 m/s². The motor has to push the whole package, not just the deck.
Example 11
Sled and kid together at 45.0 kg, towed up a gentle rise at 0.4 m/s²: a proper winter workout for the parent.
Example 12
A loaded warehouse dolly of 220 kg nudged up to just 0.3 m/s²: slow going, but you still have to lean into it.
Frequently asked questions
How many newtons is 1400 kg at 1.8 m/s²?
F = 1400 × 1.8 = 2520 N. That is the net force for that a, not engine power and not a tire-friction sum.
How is mass different from weight?
Mass is in kg. Weight is a force near m·g, in newtons. 80 kg is about 785 N at g = 9.81. Type kilograms in the mass field.
Which units do I type?
Mass in kg, or lb after the switch. Acceleration in the labeled unit, usually m/s². Result in N.
Is negative a an error?
No. Negative a is braking. Force points the other way, with a minus. 1400 kg at −7 m/s² is near 0.7 g.
Is 80 kg on a scale 80 N?
No. 80 kg is mass. Weight is about 785 N. If a problem gives newtons, divide by g before you fill the first field.
Where are friction and drag?
The formula computes the net force for the chosen a. It does not split a force budget. You assemble the parts yourself before you type a.
Where do I get distance at this a?
On the accelerated-motion page. Here it stays F = m·a, one number in newtons.
Does a comma in 1.8 work?
Yes. 1,8 and 1.8 are the same acceleration. The calculator does not require a period.
What if mass is 0 kg?
F = 0 N. There is nothing to accelerate. A minus in mass is rejected.
Is 1400 kg at 3.5 m/s² twice 2520 N?
No. 1400 × 3.5 = 4900 N. a rises from 1.8 to 3.5, not by a factor of two.
Knowledge sources
The formula is the school one. Units follow SI; NIST SP 330 and BIPM define the measures, not your result.
Page updated in 2026.